1. Field of the Invention
The present invention relates to a zoom lens system and an image pickup apparatus including the same. The present invention is suitable for, for example, a video camera, a digital still camera, a monitor camera, a silver-halide film camera, or a broadcasting camera.
2. Description of the Related Art
In recent years, image pickup apparatuses using a solid-state image pickup element have been becoming more sophisticated in functionality and smaller in size. As a photographing optical system that is used in those image pickup apparatuses, a zoom lens system having a high zoom ratio and small size is demanded.
In order to realize downsizing of a camera and a high zoom ratio of a zoom lens system, there is known a retractable zoom lens system in which an interval between lens units becomes smaller during a non-photographing period than during a photographing period so that the zoom lens system is housed in the camera body during the non-photographing period. In addition, there is known an optical-path bending zoom lens system including a reflecting member for bending an optical path of a photographing optical system by 90 degrees, so as to reduce camera thickness.
U.S. Pat. No. 7,382,548 and Japanese Patent Application Laid-Open No. 2007-279541 disclose a zoom lens system having a zoom ratio of approximately 6 to 10. Specifically, the zoom lens system includes, in order from the object side to the image side, positive, negative, positive, and positive refractive power lens units. A first lens unit and a third lens unit move for zooming. A bending unit for bending an optical path is disposed between a second lens unit and the third lens unit. Japanese Patent Application Laid-Open No. 2008-191291 discloses a zoom lens system that includes, in order from the object side to the image side, positive, negative, positive, negative, and positive refractive power lens units (five lens units). A reflection unit for bending the optical path is disposed in a first lens unit or a second lens unit.
In general, downsizing of a zoom lens system can be realized by increasing refractive power (optical power or reciprocal of focal length) of each lens unit constituting the zoom lens system and by reducing the number of lenses. However, the zoom lens system having such structure has a disadvantage that thicknesses of lenses increase for securing edge thickness due to increases in refractive powers of lens surfaces, and in particular, a front lens effective diameter is increased. As a result, it is difficult to reduce a total lens length. In addition, at the same time, more aberrations including chromatic aberration occur at the telephoto end, and hence it is difficult to correct these aberrations.
Therefore, it is important to appropriately set lens structure of the zoom lens system and to appropriately set location of the reflecting member in the optical path and movement amounts of the lens units in the zooming. In particular, if refractive powers of the lens units or movement amounts of lens units for magnification-varying in the zooming operation are not set appropriately, fluctuations of the aberrations increase in the zooming operation. In addition, it becomes difficult to downsize the entire lens system.